Echinoderms are keystone organisms that have representatives in virtually every marine ecosystem. They possess a number of features that makes them an excellent model system, namely 1) their susceptibility to changes in the chemistry of seawater and temperature 2) their ossified skeletons are major contributors to many carbonate formations 3) their variety of life history strategies that enable successful reproduction (e.g. asexual reproduction, fission, cloning and regeneration). In most parts of the ocean, CO2 and temperature co-vary, making it difficult to extrapolate isolated effects of any one variable to natural scenarios. Laboratory and field work was conducted to assess the physiological and biogeochemical response of sea urchin Psammechinus miliaris larvae to changes in water carbonate chemistry. This study used two approaches: 1) the incubation of the larvae with naturally CO2-enriched deep-seawater, and 2) the study of the effect of ocean acidification and ocean warming. It is reported that there was no effect of in situ naturally high CO2 seawater, or laboratory induced CO2 concentrations, on larval physiology or morphology. However, elevated CO2 was found to cause a decrease in fertilization and calcification. An increase in temperature appeared to counteract significantly the negative effect that high CO2 has on fertilization and biocalcification. Therefore, it is argued that the developmental stages of sea urchins may adapt to predicted ocean acidification and increasing temperature scenarios, which is advantageous to maintaining stability and survival of populations under environmental selection pressure. Furthermore, the regeneration capability of the Pacific seastar larvae Pisaster ochraceus and Orthasterias koehleri was investigated. The successful complete re-growth of the larvae can be considered a specific developmental strategy that facilitates the species’ survival. This research suggests that echinoderm larvae are resilient to conditions in a changing ocean, due to their high acclimation capabilities and to their reproduction life history strategies. In this context, echinoderms may be considered an evolutionary success.

There is no longer any part of the ocean that is inaccessible, however, spanning 361 million km2 across the earth's surface and, with approximately 50% of its volume at a depth greater than 2000 m, it is the very sheer size and complex nature of the deep ocean, that means it still remains one of the least understood environments on earth. Deep-sea hydrothermal vents are insular and ephemeral sea oor habitats that host locally abundant populations of vent endemic taxa, supported by in situ primary production through chemolithoautotrophy. Since the initial discovery along the Galapagos rift in 1977, global vent communities have been shown to exhibit significant variation in the taxonomic composition of their assemblages and, as a result, a number of biogeographic provinces have been proposed. In 2009, the ChEsSO consortium (Chemosynthetic Ecosystem Science in the Southern Ocean) initiated a three-cruise program for the discovery and exploration of chemosynthetic environments south of the Polar front. One of the major findings was the discovery of the E2 and E9 vent fields on the East Scotia Ridge (ESR), revealing faunal assemblages distinct from those of other vent biogeographic provinces. Using precision high-definition ROV videography to create broad-extent mosaic images, this thesis examines the spatial dynamics and ecological processes that govern the zonation of the faunal assemblages associated with the Antarctic vent environment. Analysis of faunal microdistribution reveals a consistent pattern of zonation with increasing distance from vent fluid exits, which can be attributed to ecological processes such as nutritional mode and reproductive development. In addition, by examining the variation in microdistribution on chimneys with differing levels of activity, suggests a possible successional sequence for vent fauna in this new biogeographic province. Finally, with over three years of visual observations, this study reveals constancy in the broad taxonomic composition of assemblages, and stability in the spatial distribution in reproductive development of dominant motile vent fauna (Kiwa n. sp.) on an intermediate-spreading ridge, which challenges the widespread perception and understanding of deep-sea vent environments.

No description available.

Submarine sediment density flows are a major process for transporting sediment from the continental shelf to the deep-ocean. Understanding submarine flow dynamics relies upon analysis of their deposits (beds) because monitoring them directly is difficult. However, it is rare to be able to correlate individual beds for long distances. This limits our understanding to ‘idealized’ models based on field data with limited lateral extent. Validation of these models requires individual beds to be mapped out. Using > 100 shallow sediment cores this thesis correlates individual beds across their depositional extent (over 2000 km), within the Late Quaternary Moroccan Turbidite System, offshore NW Africa. The vertical and spatial distributions of facies and grain size are examined in each bed to understand the dynamics of the parent flows. The height to which deposits drape up topography is used to infer flow thicknesses. Proximally, synchronous flows passed into the system from multiple disparate entry points. Earthquakes could have triggered these flows. However, it is not possible to determine if these beds were related to earthquakes, highlighting the difficulties faced extending turbidite palaeoseismology beyond the historical earthquake record. Across the central parts of the system flows are interpreted to have been relatively thin and slow moving, yet able to run out for hundreds of kilometers on slopes of < 0.02º. Current, models cannot explain how this is possible. Distally, channels develop and connect two basins. Examination of these channels reveals they are purely constructional features. Flows were able to bypass > 100 km3 of sediment through the channel axes without eroding. Channel relief was built and maintained by deposition along the channel margins and no erosion. The distribution of grain-size breaks is examined within individual beds across the entire system. Grain-size breaks between sand and mud occur almost everywhere. This is attributed to fluid mud layers bypassing intermediate grain sizes down slope. Such a process should (almost) always occur; hence this type of grain-size break should be recognized as a typical feature rather than an exception. The ability to map out individual beds over such distances provides a rare and valuable opportunity to validate models; developed from laterally restricted outcrops, laboratory experiments and theory. Results from this thesis demonstrate current models are limited and that we still have much to learn about the dynamics of submarine flows and how they transport sediment across vast swathes of the seafloor.

This research presents a detailed study of the planktonic foraminiferal records of eleven sediment cores taken from a west-east transect in the Mediterranean Sea. Correlations are based on biostratigraphy, oxygen isotope stratigraphy and assisted by AMS 14C dating. This study assesses the potential to define a foraminiferal biostratigraphy of basin-wide validity. Principal Component Analysis (PCA) is used to determine variabilities in the planktonic foraminiferal records. The first principal component groups species on its positive and negative sides in such a way that this axis may be interpreted as an expression of SST variations. This interpretation is corroborated by its close similarity to oxygen isotope records. Mean PCA scores confirm previous observations that the temperature gradient in the eastern Mediterranean basin follows the same eastward increasing trend at glacial times as it does today. In contrast, the inferred sea surface temperatures (SST) from the western Mediterranean basin suggest a reversed gradient compared to the present. Preliminary results are discussed from the unprecedented high resolution marine records from two eastern Mediterranean cores. Based on PCA and planktonic foraminiferal ratios of warm, oligotrophic mixed layer species relative to cool, more eutrophic species, a series of cool episodes is observed throughout the Holocene. The cyclicity of these events is calculated at approximately 1300 years, a figure comparable with Holocene climate fluctuations recognised previously in the North Atlantic Ocean and the Greenland Ice Sheet. Micropalaeontological investigation of two western Mediterranean cores shows for the first time that abrupt cold spells, associated with Atlantic Heinrich-events, affected the Mediterranean Sea. Unusually high abundances of the subpolar species N. pachyderma (leftcoiling) in the Gulf of Lions reflect a thriving of a normally rare taxon in the western Mediterranean, in response to distinct, short term, episodes of favourable habitat development.

Submarine flows can transport huge volumes of sediment across the large submarine fans that dominate many parts of the deep ocean floor. Active flow events are notoriously difficult to monitor directly, and therefore our understanding of such flows still strongly relies on the analysis of the deposits they leave behind. This thesis aims to investigate the transport and depositional processes, the stacking patterns and the time frequency distribution of turbidites and debrites deposited in the Miocene Marnoso Arenacea Formation (Italian Apennines). This location is unique because deposits from individual flow events (beds) can be traced for long distances, allowing the lateral and down flow evolution of single flow events to be analyzed in detail. Lateral changes in individual flow deposits are documented through extensive correlation of beds deposited in a stratigraphic interval below the most prominent Contessa Marker bed. The observed transitions in facies, and the external shape of different types of deposit, are used as an independent test of models that capture our understanding of submarine flow processes. This work highlights how deposits of submarine density flows can be complex, even in relatively simple basin plain settings. A single event can comprise different flow types, and transformations can occur between these flow types. The initial volume, sediment concentration and grain size (including the proportion of fine cohesive mud) control the external shape of the deposits. Low density turbidity currents deposit clean sandstone beds with an exponentially tapering shape, while coarser grained high density turbidity currents produce massive or parallel laminated layers that maintain their thickness for longer (10’s of kilometers) distances. Cohesive debris flows form istinctive ungraded mud-rich sandstone that can either pinch-out abruptly or gradually taper. Liquefied debris flows with elevated pore pressures can deposit clean (mud-poor) sand over large areas (up to 30 km) of the Marnoso Arenacea basin plain. This is suggested by the distinctive swirly, patchy fabric of a particular type of clean sandstone, that records pervasive liquefaction during the late stages of the flow, and confirmed by the rapid pinch-out geometry of flow deposits at their margins. Such debris flows most likely form through transformation from an initial high density turbidity current. A similar flow process may characterize the distal, rapid pinch out of sandstone lobes in Fan 4 of the Skoorsteenberg Formation (Karoo basin, South Africa). The observed stacking pattern of turbidite beds in a 530 meters thick stratigraphic section indicates a long-term clustering. Debrite intervals however occur randomly, and bed correlation suggest that almost every large volume flow deposited clean or muddy debrite (or both) intervals in different positions of the basin. Hemipelagic marl thickness is used as a proxy for time between flow events. The distribution of time between events is exponential, therefore related to a Poisson Process. This indicates that flow events (most likely triggered by submarine slope failures) occur independently one from the other through time.

This thesis presents an investigation into the reproductive processes of a collapsing population of the European flat oyster Ostrea edulis in the Solent, UK. Oyster populations are in decline worldwide. Their ecological and economic importance requires research to address the many uncertainties still existing regarding their reproduction and recruitment, in order to manage or restore populations successfully. The Solent oyster population supported a productive local fishery from 1972 to about 2006, when catch rates started to decline sharply until the fishery became economically unviable in 2011. Recurrent recruitment failures suggested that the collapse might have been caused by a disturbance of the reproductive processes. This study set out to determine if the reproductive processes were indeed inhibited, and if so, at which life history stage. Population fitness was good and gave no reason to assume that the oysters were incapable of successful reproduction due to poor condition. Histological and visual examination of the reproductive status of 362 animals revealed a significant skew towards male phase oysters (chisquare, P 0.001), while gametogenesis as such was normal in each gender. Fecundity was similar to literature values. No relationship was found between the recruitment failures or the sex ratio shift and prevalence of bonamiosis, as only two animals of the 25 examined with a PCR assay were infected. Ostrea edulis larvae were found in the plankton with a peak of 9 larvae 100 l-1 in August 2010. Larval abundance was within the range of previous records for the Solent from 1984-87. Development of Ostrea edulis larvae cultured in the laboratory was found to be normal. No apparent adverse effects of exposure to air with an increased pCO2 of 1500 atm were found either, leading to hope that the long term viability of the species will not be jeopardized by ocean acidification. No spat settlement was observed in this study. Predation pressure from Ocenebra erinacea was found to be low, and hopefully would not jeopardize restoration attempts. Overall this study showed that while there is a lack of females in the Solent oyster population, the reproductive processes as such function well enough to enable regeneration and maintenance of the population. This study demonstrated the importance of investigating the reproductive processes of a population before planning its regeneration, but it also showed that the basic factors of habitat destruction and unsustainable �shing pressure must not be overlooked.

Submarine landslides are one of the most important processes for moving sediment across our planet. Landslides that are fast enough to disintegrate can generate potentially hazardous tsunamis, and produce long run-out turbidity currents that break strategically important cable networks. It is therefore important to understand their frequency and triggers. This thesis aims to do so using extensive datasets (N>100) suitable for statistical analysis. The influence of temporally non-random variables on landslide and turbidity current frequency is assessed statistically. In light of predicted future global and sea level rises this is a timely study. Analysis of large volume turbidites (>0.1 km3) reveals two distinct frequency distribution forms for submarine landslide recurrence. A Poisson (time-independent) form is observed in three basins which may indicate similar controls on landslide frequency and triggers occur in disparate areas. A log-normal (time-dependent) distribution is seen in the Iberia Abyssal Plain over much longer timescales (20 Myr). Physiographic and palaeoclimatic effects are thought to explain the two different distribution forms. The influence of sea level is either shown to be statistically insignificant (Poisson form) or has a significantly delayed (~1.2 Myr) influence (log-normal form) on landslide and turbidite recurrence. Two sequences that cross the Initial Eocene Thermal Maximum (IETM) hyperthermal, show a reduction in turbidity current and landslide activity, rather than the increase hypothesised by many studies. Therefore, predicted future sea level rise and global warming may not necessarily result in significantly increased submarine landslide or turbidity current frequency on human timescales. Finally, a unique direct monitoring dataset from the Squamish Prodelta, British Columbia provides new insights into the links between rivers and offshore deltas on very short (<months) timescales. It is shown that elevated river discharge is the primary control for the ‘switch on’ of turbidity current activity, but the trigger for flows is related to a combination of tide and river-controlled elevated shear stresses on the submarine delta top. Extreme flood peaks do not correspond to hyperpycnal flows, but instead cause rapid accumulation of sediment leading to delta lip failures.

This study applies a metapopulation dynamics approach to modelling a distribution of plankton by representing a region of ocean as an ensemble of plankton populations interacting through the stirring and mixing eects of the ow. The methods of synchronisation theory are applied within this framework to gain insight into emergent spatial structure in biophysical simulations. The manifestation of synchronisation, including statistically stable local clustering of populations, frequency-locking or phase-locking of the entire ensemble and fully synchronised dynamics, is found to depend upon: the biological model used; the strength of mixing between populations; the number of populations or, equivalently, spatial resolution of the modelled region; the level of mismatch between and spatial arrangement of population natural frequencies; the strength of stirring of the ensemble at spatial scales larger than the grid-cell. The study therefore highlights a number of biophysical modelling parameters determining the properties of emergent spatial structure in simulations of surface ocean biological dynamics. This study shows that persistent spatial heterogeneity (patchiness) can result from what intuitively should be a homogenising in uence: mixing can increase the level of disorder between the plankton populations. Furthermore, the work shows that synchronisation eects occur generically under a range of simulation scenarios, giving condence that synchronisation theory can explain some of the spatial structure, or `patchiness', observed in plankton distributions, and providing one possible answer as to how populations of planktonic organisms maintain coherent spatial structures under the mixing and stirring action of the oceanic flow.

Submarine mud volcanism is an important pathway for transfer of deep-sourced fluids enriched in hydrocarbons and other elements into the ocean. Mud volcanoes (MVs) occur in abundance on all oceanic plate margins, so fluxes of methane (CH4) and other chemical constituents from mud volcanism are likely to be significant for the oceanic budgets of some elements. Here, I present a detailed study of the spatial and temporal variation in fluid and chemical fluxes and mud flow activity at the Carlos Ribeiro and the Darwin MVs in the Gulf of Cadiz. Analyses of the chemical composition of pore fluids, sediments and authigenic carbonates are combined with a 1-D transport-reaction pore fluid model. Pore fluids from both MVs contain high concentrations of hydrocarbons (up to 16 mM), while pore fluids from Carlos Ribeiro MV (CRMV) are also enriched in lithium (Li+) and boron (B) but depleted in chloride relative to seawater. Oxygen, hydrogen and strontium isotope data suggest that the pore fluids are derived from depth and are affected by the transformation of smectite to illite. This process also produces pore fluids that are depleted in chloride and potassium, while B and Li+ appear to be leached from the sediments during this transformation process. The CRMV is the most active of the two MVs: fluid flow velocities are as high as 4 cm yr−1 at the eye of the MV but rapidly decrease to 0.4 cm yr−1 at the periphery. The associated fluxes of B, Li+ and CH4 are 7-301, 0.5-6 and 0-806 mmol m−2 yr−1, respectively. Fluid flow velocities at the Darwin MV are lower, ῀0.09 cm yr−1, and show little spatial variation: seepage activity appears to be controlled by the distribution of slabs of authigenic carbonate that are found on the seafloor at the summit of the MV. Results of radiocarbon dating of the hemipelagic sediments covering the CRMV suggest that there has been recent mudflow activity at the eye of the MV, and frequent mud expulsions over the past ῀1000 Cal yrs BP. The distribution of barite fronts at the margin of the MV and within the mudflow to the SE of the summit suggests that fluid advection has ceased over the past 340 Cal yrs, but degassing of these mudflows is ongoing and is potentially an important source of CH4. Geochemical and petrographic analyses of carbonates from the Darwin MV suggest that the MV formed in stages, with periods of intense fluid flow alternating with phases of mud extrusion and tectonic uplift. The results of this study demonstrate that fluid (and chemical) fluxes from MVs vary over relatively small time and space scales and that mud volcanism may contribute significantly to the oceanic inventories of Li+ and B. Moreover, anaerobic oxidation of methane appears to be an important control on methane emissions into the overlying water column, and a better understanding of this process is urgently required to properly quantify the impact of mud volcanism on the global oceanic methane budget.